1. Field of the Invention
The present invention relates to a wiring circuit board having bumps, where the bumps are of a uniform height, and a method of manufacturing the same.
2. Description of the Related Art
Microscopic bumps (for example, bumps being a diameter of 50 xcexcm and a height of 30 xcexcm) are widely used when connecting electronic components such as a semiconductor device and a liquid crystal display device to a wiring circuit board, or when connecting the layers of a multi-layer wiring board.
A typical method of forming bumps of this size is shown in FIGS. 5A to 5E.
Specifically, first, as shown in FIG. 5A, a 2 layer flexible board 53 is made up of a polyimide film 51 on a copper toil 52, and copper toil 52 is patterned by photolithography to form a wiring circuit 54 (FIG. 5B).
Next, a cover coat layer 55 is formed on wiring circuit 54 in accordance with conventional methods (FIG. 5C). For example, cover coat layer 55 can be formed by forming a polyamic acid layer on wiring circuit 54, patterning by photolithography, and imidization. Alternatively, a resist ink may also be printed thereon.
Next, the area on polyimide film 51 that corresponds to wiring circuit 54 is irradiated with laser light to form bump holes 56 (FIG. 5D). Then, after covering cover coat layer 55 with a protective film as needed (not shown in the Figures), microscopic bumps are formed by growing metal bumps 57 by means or electrolytic plating on the portions of wiring circuit 54 that are exposed in the bottom of bump holes 56 (FIG. 5E).
However, when opening bump holes 56 by means of laser irradiation, there is a problem with variations in open space due to variations in the amount of smear adhered to the bottom of bump holes 56, and as a result, there is a problem with large variations developing in the height of metal bumps 57. Because of this, stable bump connections are difficult. In particular, connecting semiconductor devices to the wiring circuit in one batch by means of ultrasound is difficult. In addition, a plating pre-treatment Is essential in order to improve the strength of the adherence between wiring circuit 54 and the metal bumps 57 formed thereon.
An object of the present invention is to solve the aforementioned problems in the prior art, make stable bump connections possible, and to provide a method of manufacturing a wiring circuit board with bumps that makes complex operations such as plating pre-treatment unnecessary.
The present inventor has discovered that bumps with a uniform height and a surface roughness on the tip faces thereof of 0.2 to 20 xcexcm can be formed by half etching a metal foil with a surface roughness of 0.2 to 20 xcexcm and a thickness that is the sum of the thickness corresponding to the height of the metal bumps and the thickness of the wiring circuit layer, to a depth corresponding to the desired thickness of the metal bumps, without performing complex operations such as plating pre-treatment, and thus stable bump connections can be realized. The present inventor has finally achieved the present invention.
Specifically, the present invention provides a wiring circuit board having bumps in which a cover coat layer is formed on a first side of a wiring circuit, an insulating layer is formed on a second side of the wiring circuit, and bumps in continuity with the wiring circuit are formed such that they project from said insulating layer, wherein the wiring circuit and bumps are integrally formed from one metal foil, and a surface roughness of the tip faces of the bumps is 0.2 to 20 xcexcm.
In this wiring circuit board having bumps, it is preferred that a metallic thin film layer consisting of a metal different from the metal foil is provided between a bump formation surface on the wiring circuit and the insulating layer, in order to improve the adhesive strength between the insulating layer and the metal foil. In particular, in the event that the insulating layer is a polyimide layer imidized from a polyimide precursor layer, it is preferred that the metallic thin film layer exhibits an adhesive strength to the polyimide precursor layer that is higher than the metal foil. In this way, the adhesiveness with the polyimide precursor layer (and the imidized layer) can be improved. A combination of copper foil for the metal foil, and a thin film of Ni, Zn, Sn or Nixe2x80x94Co alloy and the like for the metallic thin film layer can be preferably mentioned as a combination for this type of metal foil and metallic thin film layer.
In addition, it is preferred that the cover coat layer has a connection aperture that allows access to the wiring circuit from the cover coat side.
In addition, the present invention provides a method of manufacturing a wiring circuit board having bumps in which the bumps formed on the wiring circuit have a surface roughness on the tip fares thereof of 0.2 to 20 xcexcm, the manufacturing method comprising the steps of:
(a) laminating a protective film on a bump formation surface of a metal foil having a surface roughness of 0.2 to 20 xcexcm and a thickness which is the sum of a thickness of the wiring circuit and a height of the bumps to be formed on the wiring circuit, and forming an etching mask for wiring circuit formation on a wiring circuit formation surface of the metal foil;
(b) half etching the metal foil from the side of the etching mask for wiring circuit formation to form a wiring circuit with a desired thickness;
(c) providing a cover coat layer on the wiring circuit after removing the etching mask for wiring circuit formation;
(d) forming an etching mask for bump formation on the bump formation surface after removing the protective film provided on the bump formation surface of the metal foil;
(e) half etching the metal foil from the side of the etching mask for bump formation to form bumps of the desired height;
(f) forming a polyimide precursor layer to cover the bumps after removing the etching mask for bump formation; and
(g) etching back the polyimide precursor layer and imidizing the same to form an insulating layer with a desired thickness. In this method of manufacturing, the wiring circuit is formed before bump formation.
In step (f) of this method of manufacturing, it is preferred that a metallic thin film consisting of a metal different from the metal foil (in particular, a metal having an adhesiveness to the polyimide precursor layer that is higher than the metal foil) is formed after the etching mask for bump formation is removed, and a polyimide precursor layer to cover the bumps is formed on the metallic thin film layer. In this way, the adhesiveness with the polyimide precursor layer (and the imidized layer) can be improved.
The present invention also provides a method of manufacturing a wiring circuit board having bumps in which the bumps formed on the wiring circuit have a surface roughness on the tip face thereof of 0.2 to 20 xcexcm, the manufacturing method comprising the steps of:
(aa) laminating a protective film on the wiring circuit formation surface of the metal foil which has a surface roughness of 0.2 to 20 xcexcm and having a thickness which is the sum of a thickness of the wiring circuit and a height of the bumps to be formed on the wiring circuit, and forming an etching mask for bump formation on a bump formation surface of the metal foil;
(bb) half etching the metal foil from the side of the etching mask for bump formation to form bumps of the desired height;
(cc) forming a polyimide precursor layer to cover the bumps after removing the etching mask for bump formation:
(dd) half etching the polyimide precursor layer and imidizing the same to form an insulating layer with a desired thickness;
(ee) forming an etching mask for wiring circuit formation on a wiring circuit formation surface after removing the protective film provided on the wiring circuit formation surface of the metal foil;
(ff) half etching the metal foil from the side of the etching mask for wiring circuit formation to form a wiring circuit with the desired thickness: and
(gg) providing a cover coat layer on the wiring circuit after removing the etching mask for wiring circuit formation. In this method or manufacturing, the bumps are formed before the wiring circuit.
In step (cc) of this method of manufacturing, it is preferred that a metallic thin film consisting of a metal different from the metal foil (in particular, a metal having an adhesiveness to the polyimide precursor layer that is higher than the metal foil) is formed after the etching mask for bump formation is removed, and a polyimide precursor layer which covers the bumps is formed on the metallic thin film layer. In this way, the adhesiveness with the polyimide precursor layer (and the imidized layer) can be improved.
In addition, the present invention provides a method of forming bumps which are formed integrally with a wiring circuit in one metal foil, wherein the bumps has a surface roughness on the tip faces thereof of 0.2 to 20 xcexcm, comprising the steps of:
forming an etching mask for bump formation on a bump formation surface of a metal foil which has a surface roughness of 0.2 to 20 xcexcm and has a thickness which is the sum of a thickness of the wiring circuit and a height of the bumps to be formed on the wiring circuit: and
half etching the metal foil from the side of the etching mask for bump formation to a depth which corresponds to the desired height for the bumps.